Real time doubling of bottom note at the octave

[Geminiclub]

I figure this would be a M4L device but what I'd like to do is play a one handed chord and have the bottom/root note doubled an octave below.

Obviously a midi effect rack/key range can archive this within a discrete range. What I'd like is for the bottom to be selected for the bass note intelligently and in any note range.

Anybody aware of any max for live patches that can achieve this?